1. Field of the Invention
The present invention relates to a lens for uniformly distributing light emitted from a light source and a light emitting device using the same. More particularly, the lens of the invention has a concave area in an outer surface thereof, formed around the optical axis, and a protrusion in a central portion of the concave surface in order to prevent a dark area.
2. Description of the Related Art
In general, a light emitting device is provided with a lens configured to distribute light emitted from a light source within a specific range. In the lens, an outer surface thereof facing away from the light source is curved convexly.
With the outer surface of the lens curved convexly, light emitted from the light source is refracted at a specific angle while it is passing through the lens to produce a light distribution range desirable to a user. However, such a lens structure has a drawback in that light concentrates on a central region of the lens around the optical axis and thereby produces an irregular light distribution.
To solve such a drawback, a light emitting device was proposed, which has a lens configured to distribute light passing around the optical axis in a wide range.
Such a convention light emitting device will now be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a vertical cross-sectional view illustrating a conventional light emitting device, and FIG. 2 is a cross-sectional view illustrating a lens of the light emitting device shown in FIG. 1.
Referring to FIG. 1, the conventional light emitting device includes a Light Emitting Diode (LED) package base 10, an LED 20 seated on an upper area of the LED package base 10 to act as a light source and a lens 30 attached to the top end of the LED package base 10 to cover the LED 20.
The LED 20 seated on the LED package base 10 emits light beams upward, i.e., toward the underside of the lens 30, which is oriented with its vertical central line aligned with the optical axis of the LED 20. The lens 30 is configured to refract the light beams emitted from the LED 20 at a specific angle so that the light beams are distributed within a specific range. Here, a convex surface 32 is formed on an outer surface of the lens 30 facing away from the LED 20, and a concave surface 34 is formed in a central portion of the convex surface 32. In a case where the convex surface 32 is formed on the entire upper surface of the lens 30, the light beams radiated from the LED 20 to the outside are concentrated around the optical axis, thereby failing to produce a uniform distribution. However, with the concave surface 34 formed in the upper central portion of the lens 30 which the optical axis intersects, the light beams diverge wide to lower brightness around the optical axis when they pass around the optical axis, thereby distributing uniformly.
In addition, the lens 30 adopted in the conventional light emitting device is so configured that the convex surface 32 has radii of curvature of 4.5 mm and 1.6 mm and the concave surface 34 has a radius of curvature of 0.6 mm as shown in FIG. 2. The concave surface 34 also has a convexed geometry in a peripheral portion connected to the convex surface 32 in order not to leave a boundary between the convex surface 32 and the concave surface 34. The convexed geometry of the concave surface 34 has a radius of curvature of 3.3 mm.
Here, the curvatures of the lens 30 shown in FIG. 2 may be varied according to the size of the lens 30. In addition, the angle of light beams refracted by the convex surface 32 and the concave surface 34 is determined by the radius of curvature of the convex surface 32 and the concave surface 34 so that the user can suitably select the radius of curvature of the convex and concave surfaces 32 and 34 according to the usage of the light emitting device.
As described above, the lens 30 of the conventional light emitting device can uniformly distribute the light beams emitted from the LED 20 since the entire upper surface of the lens 30 is composed of curved regions without any boundaries between the regions.
However, with the conventional lens 30 of the afore-mentioned structure, light passing through the concave surface 34 is dispersed laterally thereby preventing a dark area around the optical axis.
In a case where the conventional light emitting device having the dark area is used for the purpose of lighting, light illuminated to a spot desired by a user leaves a relatively dark central area. This makes it inconvenient to use the conventional light emitting device for the lighting. In addition, where the conventional light emitting device is used for a display unit, it does not provide a bright display when seen from the front.